Recently, requirements for heat-resisting materials used as structural members or components of a high temperature apparatus, such as a heating furnace, heat-exchanger, burner of heating equipment, automobile exhaust converter etc., have become more severe. As structural members or components of such apparatus, the heat-resisting materials are required to have various properties including oxidation resistance, good cold-workability, weldability and high mechanical strength at ambient temperature and even at high temperatures. Oxidation resistance in this context means not only less oxidation during usage at high temperatures but also the absence of peeling off of scales even after being subjected to cyclic treatment of heating to high temperature and then cooling to ambient temperature. Good cold workability is also required to work the material into an article having a complicated shape.
Since the structural members or components mentioned above are usually to be mass-produced, the cost of the material should be as low as possible and cost is an important factor in the development of a new high temperature material.
It is usually possible to improve one particular property of a metallic material by adding thereto a large amount of a particular element. Taking a heat-resisting steel for instance, the addition of a large amount of Cr, Si or Al may be expected to give a significant improvement in its heat resitance. However, as is known in the art, if a large amount of Cr, Si or Al is added, properties other than heat resistance are inevitably sacrificed and the result is a significant impairment of workability or weldability.
On the other hand, if we disregard cost, there are Ni-based alloys, for example, which are excellent not only in high temperature-oxidation resistance but also in other properties. However, they are so expensive that they are not suitable for use as materials for mass produced articles.
With all the above factors and conditions in mind, it is thought that the most practical and advantageous way to get a desirable heat-resistant material is to improve a specific desired property of a widely used and relatively less expensive conventional material without impairing its inherent characteristics.